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Anyone make any recommendations? I have a few simple tube amps that I'd like to learn how to bias/mod a bit but don't really know where to start...

What level are you looking at? Outright beginner, some electronics experience but not amp experience, or a general overview of different types of components and circuits?

Well, I'd have to say I'm in the beginner category. I can tell you the difference between a capacitor and a resistor and a tube...but not much beyond that. I know that there are some caps that can cook you...but don't know which ones. I took an electricity/electronics course in high school, but haven't applied much of that knowledge over the last 11 years.
I really just want to learn how to match tubes, bias amps, and some simple rewiring stuff. Nothing major, but I'm sure those things have their own peculiarities.

Before you go poking around at all, make sure you drain the power supply cap where B+ attaches. Some caps can hold a charge for a long time and you can get the jolt of your life if not careful. Use a screwdriver or other insulated on one end tool to ground the cap to the chassis, sometimes it will spark, this is good, it means it's safe to touch. I've been shocked pretty good a couple of times and it is not fun.

There are a lot of great sites on amps out there for study. I would consider finding a good simple kit amp to build, like a five watt SE amp to get your feet wet on wiring and grounding technique, then your amps will seem less mysterious.

Keep one hand in your pocket if you decide to touch anything in your amp!

A Desktop Reference of Hip, Vintage Tube Amplifiers - Gerald Weber

RCA Tube Receiving Manual (Antique books has this)

The first is a great, readable start. The 2nd is the reference you're going to want to have handy when you've learned enough to start messing with a project amp.

I really like The Ultimate Tone, by Kevin O'Connor. I have the first book and also part 3. They've been invaluable in my learning about amps, and specifically about the things you've asked about as well.

How to Service Your Own Tube Amp: A Complete Guide for the Curious Musician by Tom Mitchell is the first book I owned on the subject. It is extremely entry level, and easy to read (a bit of theory on how shit works, but for the most part it is written in a very hands on format.) There are some common mods in there, as well as some common 60's-70's amplifier tube pinout voltage charts that have come in very handy for me more than once.

this is incredibly important advice:

Before you go poking around at all, make sure you drain the power supply cap where B+ attaches.

as it is not uncommon for these caps to store voltages above 400V.
once you have done this, it is also not a bad idea to attach a bleeder resistor to the plate pin (1 or 6 on any preamp tube) so that the electrolytic capacitors do not "build back" some (potentially large) portion of their original charge. Just make sure you remove it when you are done working and ready to turn the amp on...

to get your feet wet on wiring and grounding technique

in general, it is a bad idea to work on your amp with wet feet;)

they need an emoticon getting electrocuted for this sort of discussion.

I agree, getting your feet wet before working on an amp is an extremely bad idea!

etch wrote:Before you go poking around at all, make sure you drain the power supply cap where B+ attaches.

Hey etch, what do you mean where 'B+' attaches? and how would I tell the power supply capacitor from others?

Related question - can you shock yourself on the older, smaller paper & wax capacitors as opposed to the 'can' capacitors?

Thanks for all the suggestions on books guys, looks like it's time to hit the library! Has anyone here ever read The How and Why of Guitar Tube Amps as "Gar" Sees It, by Gar Gilles?

so many questions...

ApeLincoln wrote:what do you mean where 'B+' attaches? and how would I tell the power supply capacitor from others?

Related question - can you shock yourself on the older, smaller paper & wax capacitors as opposed to the 'can' capacitors?

B+ or HT (high tension) refers to the the high voltage used by the valves. There are associated caps which filter mains to provide this B+ voltage and these are found in the power supply section. They should be drained before work ideally.

Generally speaking, you'd only expect to receive a bad shock from a larger electrolytic can capacitor found in the power supply section. You can locate these by using a schematic or by tracing what you can see in the circuit from the mains incoming.

Rather than jump straight into valve amp theory/maintenance, I'd suggest you study a little basic electronics first as otherwise you may well find yourself kind of half-knowing bits and bobs and ending up never fully sure about what you are doing.

Something like this might be good for starters:

http://www.electronics-tutorials.com/ba ... ronics.htm